i#2107: work around Android signal delivery issue
i#2107: work around Android signal delivery issue

Repeats the first instruction in master_signal_handler to work around
strange observed behavior where control is sometimes sent to the 2nd
instruction instead of the handler entry point.

Review-URL: https://codereview.appspot.com/315180043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio